Adjustable index arm for measuring instruments



Nov. 10, 1953 w H. L. BOWDITCH 2,658,469

ADJUSTABLE INDEX ARM FOR MEASURING INSTRUMENTS Filed Sept. 2, 1952 2 Sheets-Sheet 1 IN VEN TOR.

FIG. I

m HOEL. L. BOWD ITCH @ZTORIVEYS Nov. 10, 1953 ow rrc 2,658,469

I ADJUSTABLE INDEX ARM FOR MEASURING INSTRUMENTS 2 Sheets-Sheet 2 Filed Sept. 2, 1952 F I INVENTOR.

HOEL L. BOWDITCH ATTO NEYS Patented Nov. 10, 19 53 2,658,469 ADJUSTABLE INDEX ARMFoR MEASURING INSTRUMENTS IIoelL; Iio'vvdito li; Eoxboro, Masa, assignt'rttirne Foxlioro Company, Foxbo'r'o'; Mass; at corpora.-

tion of Massachusetts Application September 2, 1952, Serial No. 367.546 z'ola imsl (or. 116-1365) 1' V This invention relates to r measuring instruments wherein an index arm unit is driven in relation to changes ina variable Condition. In particular, this invention relates to anew and improved index and arrangementfor use in such instruments as, for example, a pointer, a set arm,

or apen arm. e

In industrial instrumentation especially, it is desirable to use lightweight and delicate driving and driven elements inorder to accurately measure small power responses to changes in variable conditions. In some, instruments it is desirable to reduce the frontal face size of the instruments in order to more efficiently use multi-instrument panel space. One methodof so reducing face sizeis to give the instrument substantial depth, and this arrangement may necessitatethe use of extra long index arms, Such arms must'be even more lightweight and delicate than previous shorter arms inorder to be as small a burden on the instrument as possible.

Extra long lightweight index arms present a problem in that unless supported substantially throughout their length, the y may sag or bend undesirably. Particularly in the case of horizontal arms with free ends, the whole index arm will bend downward and rest a substantial part of its weight on some part of the instrument. Such a condition introducesundesirable friction into the operational movement of the index arm. In pen arm arrangement, such a condition may produce undesirable pressure on the pen. In the ca-se of vertically disposed arms it may be difficult to properly position or apply pressure to a free end of a long';lightweight index arm. It is an object of this invention to provide adjustment means for a long, lightweight index arm. Index arms as driven or driving elements in a measuring instrument ordinarily movein a single, predetermined plane. It'is a further object to provide pivotal imovement ofsuch arms in a plane substantially at'right angles to the predeterminedoperational plane. I

It is a further obiect'to provide an index arm structure'in whichthe above m'entioned'pivotal arrangement includes means providing for easy assembly or disassembly of the index arm.

These and other objects of this invention will be in part pointed'out and will be in'part'obvious from the text and claims here presented and. from the accompanying drawings, in which: Figure I is a fragmentary perspective showing of a measuring instrument incorporating an index arm unit embodying this inventionj FigureII is aside elevation of the indexarm unit of Figure I Figure ,III is an enlargement of, a portion .of the structure of Figure II, as indicated in Figure II by the numeral III;

. Figure. IV is a plan view of one separable portion of the index arm unit of Figures I, II, and III; and I ,7,

Figure V is a plan view of another. separable portion of the index arm unit of Figures I, II, and. III. V

Referring to Figure'I, an index arm unit 10 is shown in association with a measuring instrument portion H. The position of the index arm unit It indicates the value of a factor that varies as an incident of the operation of the instrument, for example, valve position in a flow control arrangement. The instrument portion II is contained in a housing I2 with a strip chart l3 mounted therein on rollers 14 and I?) to be driven in association with a recording pen I6 for recording the measurement action of the instrument. This instrument is shown simply for the purpose of showing a typical application of the index arm unit .10. The details of the instrumerit are therefore not shown. Any of the usual strip chart recording structures may be used for this purpose. However, the index arm unit It is shown broken to indicate substantial length, greater than usual in measuring instrument index arms. This extra long index arm unit is an indication-that one'application of the index arm unit of this invention is its use in an instrument where the frontalface size is reduced by giving the'instrument substantial depth." Desirable instrument design in such a case may dictate. that the index arm units be driven from the rearof the'instru'ment,thus requiring extra long, extra lightweight index arm units. 7

The iristru ment portion u is shown with a double index scaleblocl; v l 'I mounted above the strip'chart l3, and a. control'setpointindicator I8 is arranged in association with oneof the 111-,

dex scales on'theblock l'l. The index arm unit. it has a free end pointer portion I9 associated with the other'inde'xscale on theblo ck l1.

The index arm uriit [9 has adriven base florv stub portion v n shaft 2i. Thefsh'a ft 2i is 'driven by" any suitable means, not own, in response to changes in a" variable condition. Thexdiriven shaft 2}, is shown in: avertical position with the index 'arm unit I!) movable in a horizontal plane thereby. The 1 5.

dex arm stub' 20 is generally in the form .of "a fiat strip' with one end bent, in a U formation with the shaft 2! extending vertically through both legs of the U formation. As a means'ofclam-ping the stub 20 to'the shaft 2|, the U formation is 2ll'which isfsecured to arotatable slotted as at 22 through the base of the U to connect with both of the shaft receiving openings in the U formation. A clamp bolt 23 is provided with a head 24 bearing on one edge of the U formation. The bolt 23 extends between the legs of the U formation and between the shaft 2| and the base of the U formation. As may be seen in Figure IV, the bolt 23 is threaded into a cover plate 25 on the opposing edge of the U formation. Thus as the bolt 23 is tightened the slot 22 is narrowed and the stub 20 is clamped to the shaft 2|.

Still referring to Figure IV, the stub 20 is provided with a pair of connector legs 26. These legs extend generally in the direction of the longitudinal axis of the index arm unit in straddling relation with respect to that axis. These legs, further, terminate in end portions arranged transversely of the index arm unit and laterally spaced from the main body of the unit. The connector legs are formed with a degree of resiliency for small movements toward and away from each other. Duplicate connector capstans 21 are mounted on the outer ends of the connector legs 26. As shown in Figure III, the capstans 21 are each formed with a central, reduced diameter, cylindrical portion 28 and with frustoconical ends 29 in tapering enlargement from the cylindrical portion 28.

Referring again to the stub 20, and to Figures I, II, and IV, an adjustment bolt 30 is provided. This bolt is mounted in vertically threaded relation with the stub 20, and extends through both sides of the U formation of the stub 20. The bolt 30 is located on the longitudinal axis of the index arm unit, and in the stub 20 at a. point adjacent the junction of the connector legs 26. This adjustment bolt has a spool-like member 3| secured to the under side of the head of the bolt, and concentric therewith, which is used as a factor in the assembly of the index arm unit H], as will be explained later herein.

Referring to Figures I and V, an index arm 32 is provided for separable assembly with the stub 20, with this assembly forming the complete index arm unit H). The index arm 32 has an elongated, lightweight flat strip as a main body, with the pointer formation l9 at the outer end of this main body, and an inner, butt end 33 as the driven and assembly end of the main body. A rigid, fiat strip connector crosspiece 34 is secured, flat to flat, to the main body of the index arm 32 at a point on that arm adjacent its butt end portion 33. The midportion of the crosspiece is fixed to the index arm 32 by a pair of rivets 35. The configuration of the crosspiece is generally in the form of a C, facing the butt end of the index arm. Each end of the crosspiece 34 is provided with a curved portion 36 for receiving the capstans 21 of the stub 20 in assembled relation. The curved portions 36 are duplicates and substantially semi-cylinders, vertically disposed, and with their open sides facing inwardly toward the main body of the index arm 32. The radii of the cylinder portions 36 are somewhat greater than the radii of the central cylindrical portions 28 of the capstans 21. Further, the thickness of the crosspiece 34 is somewhat less than the length of the central cylindrical portion 28 of the capstans 21. Lastly, the distance between the centers of the curved portions 36 is established as somewhat less than the distance between the centers of the capstans 21 in the unrestricted, unassembled condition of the stub 20 and its connector legs 26.

The above structural details simply mean that the index arm 32 and the stub 20 are detachably connectable in a snap action assembly, through the assembly of the index arm crosspiece 34 with the stub capstans 21, by means of the containment of the capstans in the crosspiece cylindrical portions 28. When the index arm and stub are so assembled, the resilient stub connector legs 26 are under constriction toward each other because the spacing of the crosspiece portions 28 is somewhat less than the unrestricted spacing of the capstans 21. Assembly or disassembly is accomplished by applying manual force transversely of the index arm, that is, laterally of the index arm as a whole. To assemble, one of the capstans 21 is placed in its associated crosspiece cylindrical portion, and the other capstan is snapped into place in the other crosspiece cylindrical portion by forcing the crosspiece about the first capstan as a pivot and constricting the stub connector legs 26 by camming ressure on the second capstan by the crosspiece.

This arrangement strongly holds the index arm and stub together and insures definiteness and duplication of alignment and of operative dimension when disassembled and replaced or reassembled.

In the assembly of the index arm 32 and the stub 20, the index arm is in effect pivoted on the stub about an axis generally indicated in Figure I by the axis line 31. The crosspiece connections to the capstans 21 provide this effective pivot arrangement because the crosspiece thickness is somewhat less than the length of the capstan cylinder 28 and because the crosspiece cylindrical configurations 36 have radii some.. what greater than the radii of the capstan cylinder 26.

Thus the index arm is driven in a horizontal plane at right angles to the drive shaft 2|, and in addition, the index arm is pivotable in a vertical plane.

In the assembly of the index arm 32 and the stub 23, the index arm butt end 33 is located between the ends of the adjustment spool 3|, and is in upwardly biased engagement with the top end of the spool. This upward bias is provided by the pull of gravity on the elongated index arm portion on the opposite side of the index arm pivot axis 31. The index arm pointer portion |9 may thus be lifted against gravity within the limits provided by the spool ends, while its downward movement is limited by the positive stop action of the adjustment bolt 33. The index arm is flexible and will bend down somewhat because of this factor, even though it is in engagement with a positive stop at its butt end. The spool ends may be separated by whatever distance is preferred for free pivotal movement of the index arm.

In the arrangement shown, the index arm may be pivoted in a vertical plane to move the indicator point It upwards by adjusting the bolt 30 downwards. This action may be used to lift the point It or simply to reduce the effect of gravity on the index arm. In some instances it may be desirable to add to the gravital effect by adjusting the bolt 33 upwards. This adjustment will result in the index arm indicator point moving downward until the index arm engages some part of the instrument. Further upward adjustment of the bolt 30 would then result in increased pressure in this index arm engagement. With an index arm in the form of a pen, this arrangement would be found useful to vary the pen pressure on a recording surface. In other arrangements. for example wherethe index arm pivot axis 31 is vertical, the adjustment bolt 36 may still be used for positioning or variable pressure application of a pen or other index arm arrangement. Similarly, the arrangement is effective where the pivot axis 31' is horizontal and the index arm general disposition is vertical.

This invention, therefore, provides a new and novel measuring instrument index arm assembly in which an index arm is pivotally adjustable with respect to a supporting stub, and in a plane at right angles to the plane of driven movement of the index arm assembly. In addition this invention provides a novel arrangement of the above assembly, with the index arm pivot arrangement thereof in the form of a snap action separable structure.

As many embodiments may be made in the above invention, and as many changes may be made in the embodiments above described without departing from the spirit and scope of the invention a described herein and shown in the accompanying drawings, it is to be understood that all matter hereinbefore set forth or shown in the accompanying drawings is to be inter preted as illustrative only and not in a limiting n u r) arm mounting comprising pairs of abutting portions of said arm and said stub arranged transversely of said arm unit and provided with elements of a resilient separable fastener arranged to be engaged and released by a force exerted transversely of said arm and when engaged serving to hold said abutting portions together,

2. In a measuring instrument, a two part index arm unit comprising, in combination, a stub which is driven in a horizontal plane in relation to changes in a variable condition, and an arm detachably secured to said stub in a snap fastener pivotal arrangement for movement of said arm in a vertical plane, said stub having a pair of oppositely and laterally extending resilient arms and a connection capstan on each of said arms, said arm having a crosspiece secured thereto and capstan receiving configurations on said crosspiece with said resilient arms biased to hold said capstans in said configurations to provide said snap fastener arrangement, and an adjustment member on said stub with a portion of said arm in operative engagement with said adjustment member due to the influence of gravity on said index arm, whereby movement of said adjustment member results in movement of said arm in said vertical plane.

HOEL L. BOWDI'ICH.

References Cited in the file of this patent UNITED STATES PATENTS Number Name Date 2,186,517 Bradford Jan. 9, 1940 2,500,557 Bowditch Mar. 14, 1950 

